Electric motor



/7/'5 A TTOHNEY Jan. 5, 1937; c. w. RlPscH I' ELECTRIC MOTOR Filed Feb;1, 1954 patented Jan. 5, 1937 UNITED STATES PATENT OFFICE ELECTRIC'MOTOR Application February 1, 1934, Serial No. 709,357

2 Claims.

This invention relates to electric motors and more particularly to amotor forming a part of a portable tool or the like. In motors of thiskind the stator is usually supported in direct con- 5 tact with themotor casing and the heat generated in the stator is transmitted to thecasing and causes the same to become Very hot. In a portable tool it isoften necessary for the operator to grasp the motor casing or his handswill often come in contact therewith and the heating of the casing ishighly objectionable. Further, it is usually necessary to remove thestator from the casing more or less frequently for the purpose ofrepairs, cleaning or replacement, and, due to the snug lit of the statorin the casing its removal will often scar or mutilate the surface of thecasing against which the stator is supported. Sometimes the attachingscrews will draw the metal of the stator outwardly around the screwholes and form burrs which will deeply scar the casing. The repeatedscarring of the casing will eventually so deform the same that it willno longer provide a proper support for the stator and the latter willvibrate or wobble in the casing.

One object of the invention is to provide a motor of a constructionwhich will prevent or materially reduce the transmission of heat fromthe stator to the casing.

A further object of the invention is to provide a motor in which thestator'will be supported in engagement with heat insulating material ofsuch a character that it will not be easily scarred by the removal ofthe stator and which may be readily renewed in the event it should beobje'ctionably scarred.

A further object of the invention is to provide amotor with a combinedheat insulating member and wear plate which can be embodied thereinwithout substantial change in the construction of the motor and at asmall cost, and which will be readily removable from the casing.

A further object of the invention is to provide a motor having a readilyremovable stator and of such a character that neither heat norelectricity will be transmitted from the stator to the casing.

Other objects of the invention will appear as the motor is described indetail.

In the accompanying drawing, Fig. 1 is a side elevation of a portabletool with the motor in section and one handle broken away; and Fig. 2 isa transverse section taken on the line 2 2 of Fig. 1.

In this drawing I have shown the invention in connection with the motorof a portable tool of a well known design but it will be understood thatthe invention may take various forms and may be embodied in motors usedon tools of various kinds,

or for other purposes. The particular portable tool here illustratedcomprises a body portion 5 5 on the upper or rear end of which ismounted a motor comprising a casing 5, stator 'I and a rotor 8 carriedby a shaft 9 which is connected through suitable driving mechanism inthe body portion 5 of the tool with a wrench HJ, or other implement, 10at the lower end of the body portion. The motor casing is provided withhandles Il one of which may embody a switch I2 for controlling theoperation of the motor.

In embodying my invention in a motor of the 15 kind here shown thecasing is made of an internal diameter slightly greater than thediameter of the stator so as to provide a narrow Space between theseparts and in this space is inserted an insulating medium of such acharacter that it will not only prevent, or substantially reduce, thetransmission of heat from the stator to the casing but will provide aneliicient wear surface which will not be easily marred or injured. Theinsulating medium may be of any suitable form and may comprise one or aplurality of sections. In the particular arrangement here illustratedthe insulating medium comprises a plurality of strips of heat insulatingmaterial spaced one from the other about the stator and held firmly incontact 30 with the adjacent surf aces of the stator and of the casing.This arrangement materially reduces the amount of insulating materialrequired, and permits the ready removal of the individual strips.Further, the spacing of the strips provides passageways for thecirculation of air to cool thel stator, but it will be obvious that whenthe stator itself is of such a construction as to provide the necessaryventilation the spacing of the strips is unnecessary. The insulatingmaterial is of a noncompressible character so that it will not yieldunder the action of the attaching devices by means of which the statoris secured to the casing, as any yielding of this material would be aptto throw the stator off center with relation to the 45 rotor. Thematerial is also very hard so that it presents to the stator a hardsmooth surface which will not be easily scarred by the removal orinsertion of the stator, the latter being removable through one end ofthe casing, in the present instance in the lower end. It is desirablethat the insulating material should be of such a character that it canbe machined in order to reduce the insulating strip to the exactthickness required to 'completely ll the space between the stator and 55the casing. rThis material also has a high dielectric strength whichwill prevent the passage of current from the stator to the casing in theevent of a short circuit in the motor. I have found that a hardnon-brittle phenolic condensation product, such as that sold under thetrade name bakelite meets all the requirements in a very satisfactorymanner and it is available in various shapes, either with or withoutreinforcing material embedded therein, but it will be obvious that anymaterial having a low heat conductivity and having the necessarycharacteristics may be used.

In preparing the insulating strip or strips I prefer to utilize a fiatannular strip or ring of suitable material of a diameter approximatelyequal to the internal diameter of the motor casing and to then machinethis ring to provide it with the desired thickness and with the properinner and outer diameters. It is not usually desii-able to extend theinsulating strip entirely about the stator and I prefer to employ aplurality of relatively short strips, three such strips being shown atI3 as spaced about the stator substantially equal distances. Therefore,after the ring has been reduced to the desired thickness, sever the sameinto a plurality of segments, I3, one ring thus providing a suiicientnumber of short strips or segments to insulate several motors. Theinsulating strips are inserted in the motor casing prior to theinsertion of the stator and are attached to the casing in such a manneras to cause them to be held in position while the stator was beinginserted. In the present instance, this is accomplished by passing smallscrews I4 through the wall of the casing and threading the same intosuitable openings provided in the insulating strips. While the screws i4may be suiicient ordinarily to retain the strips in position during theinsertion and removal of the stator I prefer to provide the casing withupper and lower shoulders I5 and I6 spaced apart a distancesubstantially equal to the width of the insulating strip so that thelatter will t snugly between the same. When the several insulatingstrips have been inserted in position as described the stator isinserted and when it has been properly located is secured within thecasing by means of suitable attaching devices. These attaching devicesare here shown as screws I1 extending through the usual screw holes inthe Wall of the casing, through openings formed in the respective stripsand threaded into the stator. The tightening down of these screws willrigidly secure the stator, insulating strips and casing one to the otherwith their adjacent surfaces in contact one with the other. If desired,the screw holes in the wall of the casing may be enlarged and bushingsI8 of insulating material inserted therein to provide for completeelectrical insulation between the stator and the casing.

The heat insulating strips being of a hard noncompressible characterwill not yield under the pressure of the stator when the screws I1 aretightened down but will serve to accurately locate the stator withrelation to the rotor, and they will not be easily scarred upon removalor insertion of the stator` However, in the event they should be soscarred they can be easily removed and renewed at small cost. It will beapparent that the combined heat insulating member and wear plate can beembodied in the motor with little or no change in the constructionthereof and at very small expense.

While I have shown and described one embodiment of my invention I wishit to be understood that I do not desire to be limited to the detailsthereof as various modifications may occur to a. person skilled in theart.

Having now fully described my invention, what I claim as new and desireto secure by Letters Patent, is:

l. In a motor comprising a casing and a stator Within said casing, aplurality of strips of hard non-compressible material of low heatconductivity spaced about said stator between the same a-nd said casingand shaped to conform to the contour of said casing, said casing havingshoulders engaging the opposite edges of said strips, and attachingmeans extending through the wall of said casing and through therespective strips to rigidly support said stator in firm engagement withsaid strips.

2. In a motor comprising a casing and a stator within said casing, aplurality of strips of hard non-compressible material of low heatconductivity spaced about said stator between the same and said casingand shaped to conform to the contour of said casing, means for securingsaid strips to said casing independently of said stator, and means forsecuring said stator to said casing and holding the same in rm contactwith said strips.

CHARLES W. RIPSCH.

